Tuesday, April 30, 2013
Exhibit Hall
The conversion of plant cellulose biomass to fuel ethanol by microbial fermentation is one of the most important priority areas of research, and the use of industrially suited microorganisms for the cost-effective biofuel production is the major technical challenge. Cellulosic ethanol would reduce the petroleum dependency, as ethanol is produced from the inexpensive and plentiful feedstocks. One of the main challenges emerging from the use of lignocellulosic feedstocks for ethanol production by Saccharomyces cerevisiae is the efficient fermentation of pentoses (xylose and arabinose), as these sugars cannot be used by natural S. cerevisiae strains, especially in the presence of inhibitors (e.g. acetic acid and furfural) that are formed during feedstock pretreatment and hydrolysis. DSM has developed industrial advanced S. cerevisiae strains that have been genetically engineered to enable the conversion of the pentose sugars to ethanol, retaining at the same time the ability to rapidly ferment hexoses. Subsequently, the utilization of pentoses was improved in these strains by applying evolutionary engineering strategies, such as e.g. sequential batch reactor cultivation, resulting in a significant reduction in the time required to completely ferment hexoses and pentoses in sugar mixtures. In addition, both rational and random approaches were pursued in order to increase cellular robustness, focusing on the improvement of acetic acid tolerance. This paper describes the work aiming at accelerating the pentose fermentation together with improving the tolerance to inhibitors in synthetic media as well as in lignocellulosic hydrolysates, at an economically relevant dry matter level.